Battle of the Frigidus

Definition: The Battle of the Frigidus, September 5-6, A.D. 394, was fought between the usurper Eugenius and his pagan supporters, including the magister equitum Arbogast, on the one side, and Emperor Theodosius I, on the other. Emperor Gratian had made his magister militum, Theodosius, emperor in the East in January 379 to replace Valens. Theodosius ruled for 16 years during which time he was baptized, and had two sons, Arcadius and Honorius, whom he made co-emperors at puberty.

Gratian sent Arbogast to Theodosius to help him against the Goths in Thrace in 380. In 384, Arbogast recovered Gaul from the usurper Magnus Maximus (whose Gothic troops had killed Gratian) for the Western emperor who had succeeded Gratian, Valentinian II. Arbogast served as magister equitum under Valentinian II. Arbogast imposed a treaty on the Franks and had become quite powerful. When Valentinian tried to remove him from power, in 391, Arbogast ignored the order, stating that only Theodosius had such authority. Valentinian II died shortly thereafter, May 13, 392, supposedly, a suicide.

Arbogast proclaimed a pagan, Eugenius, the magister scrinii, Emperor in the West. In 394, Theodosius marched west to deal with both the usurper and the restoration of paganism. At the Battle of the Frigidus River (now, Vipava River), in the Alps, two days of fighting resulted in the victory of Theodosius, the beheading of Eugenius the usurper, and the suicide of Arbogast.

Sources include the Encyclopedia Britannica